Suture anchors are used in orthopedic surgery to, for example, reattach a ligament to a bone after the ligament has been separated from the bone by a sports injury. Suture anchors are inserted into the bone and include barbs, threads or other means to resist pullout force applied to the anchor. Anchors typically include an eyelet or other structure to secure a length of suture. The suture is used to draw a ligament against the bone. With the ligament held to the bone, preferably at or near the original attachment point, the ligament is able to reattach to the bone. Suture anchors are normally made of either a bio-absorbable compound or a bio-compatible material because the anchor is often covered by the reattached ligament once the healing process is completed and cannot be easily removed.
Suture anchors can be either removable or non-removable after initial placement. Non-removable suture anchors are typically hammered or pushed into the bone, either with or without a pre-drilled hole, and retained by barbs that resist pullout. Removable suture anchors are typically threaded and may be screwed into the bone for anchoring and unscrewed from the bone for removal. Some removable suture anchors include a hole-starting drill bit that bores a hole in the bone ahead of the threaded portion. This eliminates the need to pre-drill a pilot hole for the anchor. One drawback of such an anchor is that, as the drill bit bores through the bone, it may migrate and the path of the hole may be widened or misdirected from the originally intended location. It is therefore difficult to accurately place self-drilling anchors.
A suture anchor is best placed as close as possible to the original attachment point of the ligament to facilitate reattachment. However, with existing anchors, this is often difficult due to interference from surrounding soft tissue or bones. The first site chosen for an anchor may be determined to be unsuitable for various reasons that may not be known until after insertion. For instance, the underlying bone structure may be incapable of supporting the anchor properly. The anchor must then be re-sited in a different location. Re-siting is impossible with non-removable anchors, multiple anchors must be implanted instead.
Removable anchors make re-siting possible but existing removable anchors have several drawbacks. Existing removable anchors create a hole, either pre-drilled or drilled by the anchor, with a diameter and a depth corresponding to the size of the anchor. The hole is generally cylindrical in shape, but may be irregular and even larger than the root portion of the anchor if the drill was not maintained at a constant angle throughout the drilling process. As a result, the bone structure is weakened around the drilled hole. If the anchor must be re-sited, the surgeon must avoid the area around the previous hole, sometimes resulting in a placement that is less than surgically optimal.
With known removable anchors, the area within a diameter of the original hole is generally precluded from re-siting for several reasons. First, there is the likelihood that a hole drilled close to the original hole would migrate into the original hole resulting in further bone structure damage and another unusable hole. Second, the re-sited hole must not overlap the original hole or the threads in the overlapping area would have no bone purchase. Third, the re-sited hole must be moved a certain distance from the first hole, around which the bone structure has been weakened, to an area where the bone structure has not been weakened so that the full pullout strength is available to secure the ligament tightly to the bone.
Preferably, an anchor should be quickly, easily and removably insertable to an assessment position while producing the minimum impact on bone structure. When re-siting is necessary, the damage to the bone at the original site should not significantly impact the surgeon's choice for a second site. Furthermore, the anchor should be predictably insertable along a path to a precise final position.
Existing drivers for removable suture anchors also suffer from a number of deficits. In particular, some drivers utilize a small hex drive to couple to the anchor, and such drives are subject to stripping wherein the comers of the hex are rounded off. The surgeon must then grab the anchor with pliers or a similar device and attempt to remove it. Existing drivers are also sometimes difficult to load with the suture. With drivers that are cannulated to pass the suture, a special tool is often required to insert the suture through the driver. This arrangement can make use of a suture with a pre-attached needle difficult or impossible. In the case of drivers where the suture extends laterally rather than up through the driver, the suture can become tangled with the driver as the anchor is driven in. In either case, the needle remains exposed during installation of the suture, with the accompanying risk of an accidental needle stick. It is therefore an object of the present invention to provide a driver that can be used with sutures with pre-attached needles. It is also an object of the present invention to provide a driver which can be used without risk of an accidental needle stick.